You can do this already with http://todotxt.com/ it works pretty well.

Thanks for the recommendation for Epistle. I use Dropbox to sync my TODO.txt between my phone, home computer, and work computer. The Dropbox default editor is mostly adequate, but is a speedbump when I just want to jot down a quick note.

I do pretty much the same thing but using simplenote. Simplenote has a lot of clients including one for vim and emacs so it's pretty easy to find one on the platform of your choice.

"Every time that I try Evernote on OS X it feels alien."

Yeah! Weird, but I get this too! What is it that makes it feel so strange on OS X?

But yeah, a text file on Dropbox is my favorite solution.

Edit: I do actually use and like todo.txt, myself. Worth getting to know.